Orthogonal Frequency-Division Multiple Access (OFDMA) is a multiple access method for sharing a radio frequency (RF) channel among multiple stations. OFDMA uses an orthogonal frequency-division multiplexing (OFDM) digital modulation scheme to modulate information signals. OFDMA can be described as a combination of frequency domain and time domain multiple access. In OFDMA, a communication space is divided into multiple timeslots and each timeslot is further divided into a number of frequency sub-channels, each having at least one of its own sub-carriers. In OFDMA systems, both time and/or frequency resources are used to separate signals to/from multiple stations, wherein transmissions to/from multiple stations are separated using timeslots and sub-channels within each timeslot such that stations' signals can be separated in the time domain and/or in the frequency domain. Thus, in OFDMA, resources can be partitioned in the time-frequency space.
Recently, broadband wireless networks have been developed that implement OFDMA, as described for example in the Institute of Electrical and Electronics Engineers (IEEE) 802.16 standards or in the Long Term Evolution (LTE) standards. As used herein, “IEEE 802.16” refers to a set of IEEE Wireless Metropolitan Access Network (WMAN) standards that govern broadband wireless access methods. Any of the IEEE standards or specifications referred to herein may be obtained at IEEE, 445 Hoes Lane, PO Box 1331, Piscataway, N.J. 08855-1331, USA. LTE is the Third Generation Partnership Project (3GPP) from the European Telecommunications Standards Institute (ETSI). LTE is used to create a high speed wireless data communications network. Any of the ETSI standards or specifications referred to herein may be obtained at 650, Route des Lucioles, 06921 Sophia-Antipolis Cedex, FRANCE.
In a wireless communication system, a near-far problem may exist. The near-far problem refers to the situation where a receiving station receives a low-power signal from a desired transmitting station and a high-power signal from a different transmitting station at the same time, resulting in desensitization or “desense” of a receiver in the receiving station to the low-power signal. In other words, the high-power signal may cause the low-power signal to fall below the receiver's detectability threshold. For instance, when the high power transmitting station is located near the receiving station operating in the same timeslot but on a different frequency sub-channel, the high transmit energy can desensitize the receiver.
Scheduling algorithms are widely used in wireless networks for allocating or distributing communication resources (e.g., timeslots and/or sub-channels) among stations to take advantage of instantaneous channel variations by giving priority to the stations with favorable channel conditions. For instance, in an OFDMA communication system, a base station can include a time-division multiple access (TDMA) scheduler that schedules time/frequency resources used by each uplink communication and each downlink communication. An uplink communication is when a station transmits to the base station and downlink communication is when the base station transmits to a station. The scheduler may assign an uplink communication on different sub-channels within the same timeslot to different stations. In particular, the base station scheduler may schedule these uplink communications either in different timeslots or in the same timeslot and uses power control to prevent/reduce near-far interference among various stations communicating to the base station. Accordingly, the TDMA scheduler avoids near-far problems by creating time-orthogonal uplink and downlink transmissions, and through uplink power control. The scheduler may assign a downlink communication on different sub-channels within the same timeslot from the base station to different stations. The near-far interference issue is avoided in that there is only the single desired transmitter and no interfering transmitter operating simultaneously. These techniques are applicable to time division duplexing (TDD) wireless communication systems where a select orthogonal portion of time has been set aside within the frequency channel for uplink and downlink transmissions and frequency division duplexing (FDD) wireless communication systems where a separate frequency channel is dedicated to uplink and downlink transmissions.
Although the TDMA scheduling techniques described above work well in situations where all stations communicate with and are assigned or scheduled resources by a central base station, these techniques do not work in mixed networks that also include direct station-to-station or “peer-to-peer” communication between stations. When one station connects directly with and communicates directly with another station, this method of communication is referred to herein as one-to-one peer-to-peer communication. With one-to-one peer-to-peer communication, there is no concept of uplink and downlink because communications links occur between the stations. When one-to-one peer-to-peer communication links are allowed to share a portion of the time-frequency resources whether within conventional uplink or downlink resource allocations of TDD/FDD networks or resource allocations occupied by peer-to-peer communication links alone, near-far interference can occur. The near-far interference can desense the base station-to-station and/or station-to-base station communication links or the station-to-station peer-to-peer links.
One-to-one peer-to-peer communication can be directed (centralized scheduling) by a base station or it can be self-directed (distributed scheduling) by the stations involved in the communication. With centralized scheduling, stations communicate with the base station via control channels to exchange information needed for scheduling. With distributed scheduling, stations communicate with each other in order to exchange information needed to schedule resources. Ad-hoc mesh networking may expand the communications range of one-to-one peer-to-peer networks, wherein mesh nodes or stations could collect and forward routing, neighbor list and other information either to a centralized base station scheduler or to stations employing distributed scheduling. OFDMA communication systems allowing one-to-one peer-to-peer communications employing either centralized scheduling or distributed scheduling with or without ad-hoc mesh networking may experience significant near-far interference. These near-far interference issues may increase if the one-to-one peer-to-peer links are allocated resources within the time-frequency map of conventional TDMA uplink/downlink schedulers.
In some systems, one station may transmit information directly to multiple peer stations. This method of transmission is referred to herein as one-to-many peer-to-peer communication. The phrase “peer-to-peer communication” is used herein for both one-to-one and one-to-many peer-to-peer communication. Therefore, in addition to scheduling one-to-one peer-to-peer communication and ad-hoc mesh communication links, an avenue is needed for scheduling one-to-many peer-to-peer communication links, without experiencing significant near-far issues as found in conventional TDMA uplink/downlink scheduling.
Accordingly, it would be desirable to provide scheduling techniques for scheduling various types of peer-to-peer communication links.
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The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.